Near-unity NIR phosphorescent quantum yield from a room-temperature solvated metal nanocluster

Metal nanoclusters have emerged as promising near-infrared (NIR)–emissive materials, but their room-temperature photoluminescence quantum yield (PLQY), especially in solution, is often low (<10%). We studied the photophysics of Au 22 ( t BuPhC≡C) 18 (Au 22 ) and its alloy counterpart Au 16 Cu 6 ( t BuPhC≡C) 18 (Au 16 Cu 6 ) (where t Bu is tert -butyl and Ph is phenyl) and found that copper (Cu) doping suppressed the nonradiative decay (~60-fold less) and promoted intersystem crossing rate (~300-fold higher). The Au 16 Cu 6 nanocluster exhibited >99% PLQY in deaerated solution at room temperature with an emission maximum at 720 nanometers tailing to 950 nanometers and 61% PLQY in the oxygen-saturated solution. The approach to achieve near-unity PLQY could enable the development of highly emissive metal cluster materials.